PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY PHILIPPE PLAILLY / SCIENCE PHOTO LIBRARY
Scanning tunnelling micrograph of a deposit of boron on a silicon substrate. The scanning tunnelling microscope (STM) uses a fine point electrode, a few atoms thick at the tip, and is capable of atomic- scale resolution. The tip is brought to within a few angstroms (a few ten- millionths of a millimetre) of the sample's surface. As the electron clouds of the tip and the sample atoms interact, a small 'tunnelling' current passes. The electrode scans across the surface, moving vertically to maintain the tunnelling current. This motion is then processed to produce a map such as that seen here.
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